1. Field
A compressor, and more particularly, a scroll compressor is disclosed herein.
2. Background
Scroll compressors are known. However, they suffer from various disadvantages.
A scroll compressor refers to a compressor that utilizes a first or orbital scroll and a second or fixed scroll having a spiral wrap, the first scroll performing an orbital motion with respect to the second scroll. While the first scroll and the second scroll are engaged with each other in operation, a capacity of a pressure chamber formed therebetween may be reduced as the first scroll performs the orbital motion. Hence, the pressure of a fluid in the pressure chamber may be increased, and the fluid discharged from a discharge opening formed at a central portion of the second scroll.
The scroll compressor performs a suction process, a compression process, and a discharge process consecutively while the first scroll performs the orbital motion. Because of operational characteristics, the scroll processor may not require a discharge valve and a suction valve in principle, and its structure may be simple with a small number of components, thus making it possible to perform a high speed rotation. Further, as the change in torque required for compression is small and the suction and compression processes consecutively performed, the scroll compressor is known to create a minimal noise and vibration.
For the scroll compressor, an occurrence of leakage of a refrigerant between the first scroll and the second scroll should be avoided or kept at a minimum, and lubricity (lubrication characteristic) should be enhanced therebetween. In order to prevent a compressed refrigerant from leaking between the first scroll and the second scroll, an end of a wrap portion should be adhered to a surface of a plate portion. On the other hand, in order for the first scroll to smoothly perform an orbital motion with respect to the second scroll, resistance due to friction should be minimized. The relationship between the prevention of the refrigerant leakage and the enhancement of the lubricity is contradictory. That is, if the end of the wrap portion and the surface of the plate portion are adhered to each other with an excessive force, leakage may be prevented. However, in such a case, more friction between the parts may result, thereby increasing noise and abrasion. On the other hand, if the end of the wrap portion and the surface of the plate portion are adhered to each other with less than an adequate sealing force, the friction may be reduced, but the lowering of the sealing force may result in the increase of leakage.
In order to solve such problems, a back pressure chamber having an intermediate pressure between a discharge pressure and a suction pressure may be formed on a rear surface of the first scroll or the second scroll. That is, the first scroll and the second scroll may be adhered to each other with proper force, by forming a back pressure chamber that communicates with a compression chamber having an intermediate pressure, among a plurality of compression chambers formed between the first scroll and the second scroll. With such a configuration, leakage of refrigerant may be prevented and lubricity enhanced.
The back pressure chamber may be positioned on a lower surface of the first scroll or an upper surface of the second scroll. In this case, the scroll compressor with such a back pressure chamber may be referred to as a ‘lower back pressure type scroll compressor’ or an ‘upper back pressure type scroll compressor’ for convenience. The structure of the lower back pressure type scroll compressor is simple, and its bypass holes easily formed. However, as its back pressure chamber is positioned on the lower surface of the first scroll, the form and position of the back pressure chamber change due to the orbital motion. This may cause the first scroll to tilt, resulting in the occurrence of vibration and noise. Further, an O-ring to prevent leakage of a compressed refrigerant may be rapidly abraded. The structure of the upper back pressure type scroll compressor is complicated. However, as the back pressure chamber of the upper back pressure type scroll compressor is fixed in form and position, the probability of the second scroll tilting is low, and sealing for the back pressure chamber is excellent.
Korean Patent Application No. 10-2000-0037517, entitled Method for Processing Bearing Housing and Scroll Machine having Bearing Housing, which corresponds to U.S. Pat. No. 5,156,539 and U.S. Reissue Pat. No. 35,216, all of which are hereby incorporated by reference, discloses an example of such an upper back pressure type scroll compressor. FIG. 1 is a partial cross-sectional view showing an example of an upper back pressure type scroll compressor. The scroll compressor 1 of FIG. 1 may include a first or orbital scroll 30 configured to perform an orbital motion on a main frame 20 fixedly-installed in a casing 10 and a second or fixed scroll 40 engaged with the first scroll 30 to create a plurality of compression chambers upon the orbital motion. A back pressure chamber BP may be formed at an upper portion of the second scroll 40, and a floating plate 60 to seal the back pressure chamber BP may be installed so as to be slidable up and down along an outer circumferential surface of a discharge passage 45. A discharge cover 2 may be installed on an upper surface of the floating plate 60, thereby dividing an inner space of the scroll compressor 1 into a suction space (S) and a discharge space (D). A lip seal (not shown) may be installed between the floating plate 60 and the back pressure chamber BP, so that refrigerant may be prevented from leaking from the back pressure chamber BP.
The back pressure chamber BP may communicate with one of the plurality of compression chambers, and may be at the receiving end of an intermediate pressure from the plurality of compression chambers. With such a configuration, pressure may be applied upward to the floating plate 60, and the pressure also applied downward to the second scroll 40. If the floating plate 60 moves upward due to pressure of the back pressure chamber BP, the discharge space may be sealed as an end of the floating plate 60 contacts the discharge cover 2. In this case, the second scroll 40 may move downward to be adhered to the first scroll 30. With such a configuration, a gap between the second scroll 40 and the first scroll 30 may be effectively sealed.
The pressure inside the back pressure chamber BP should be maintained at a level that enhances the sealing of the leakage while minimizing the friction between components. However, in a case in which the pressure inside the back pressure chamber BP is higher than a discharge pressure due to change in an operating condition of the scroll compressor, or in a case in which the pressure inside the back pressure chamber BP is drastically increased when the compressor is initially operated, the refrigerant inside the back pressure chamber may excessively press the second scroll, thus resulting in noise and abrasion due to friction between the components. In this case, the refrigerant should be discharged outside so as to reduce the pressure inside the back pressure chamber BP. In the conventional art, the refrigerant inside the back pressure chamber is discharged to the discharge space through a lip seal.
However, when the scroll compressor having such configuration is applied to an air conditioner for both heating and cooling, there occur problems. More specifically, during a heating operation, when a defrosting process should be performed to defrost a condenser of an outdoor unit or device, or when the heating operation is converted into a cooling operation, a size of the suction pressure and a size of the discharge pressure of the scroll compressor are reversed from their normal configuration. That is, right after the change in the operation mode, the suction pressure becomes higher than the discharge pressure.
As the pressure inside the back pressure chamber becomes higher than the discharge pressure, the refrigerant inside the back pressure chamber is rapidly discharged through an entire inner circumferential surface of the lip seal, until the pressure inside the back pressure chamber becomes equal to the discharge pressure. As an upper surface of the floating plate is disposed in the suction space, an upper pressure of the floating plate becomes higher than the pressure inside the back pressure chamber. At the same time, the floating plate moves downward, while the second scroll moves upward by a suction pressure. That is, as the gap between the second scroll and the first scroll is widened due to the anomaly of the sucking pressure and the discharge pressure, the first scroll tilts during its operation, thus resulting in noise and vibration. In order to solve such problems, U.S. Patent Pub. No. 2012/0107163, which is hereby incorporated by reference, discloses a compressor seal assembly in which a hole is formed at one side of the back pressure chamber to communicate the back pressure chamber with the suction space, and an Injection Pressure Regulator (IPR) valve formed of springs and balls is installed at or in the hole. With such a configuration, in a case in which the pressure inside the back pressure chamber is higher than the pressure of the suction space by a predetermined amount, the refrigerant inside the back pressure chamber is discharged to the suction side. Therefore, in a case in which the pressure inside the back pressure chamber is excessively high, the pressure inside the back pressure chamber may be reduced using the valve.